Counter mechanisms are known in which an input typically drives a lowest order number wheel and, where the number being counted is to be expressed in the decimal system, the lowest order number wheel transfers a "carry-over" movement to the next order number wheel when the number nine changes to zero. Similar transfer movements are provided for the number of wheels of the other orders. So-called Geneva mechanisms can be used to provide the required operation.
In postage meters, counter mechanisms are required to maintain an account of certain quantities, such as the total value of postage printed, the value of postage credit remaining, and the like. However, since the postage value can involve several orders, the counter mechanism must be capable of accepting count inputs to several of its lower order number wheels, as well as including the facility to carry over a single digit movement to the next order number wheel when the number nine is exceeded. One such mechanism is disclosed in U.S. Pat. No. 2,774,537 (Russell et al), in which differentially geared number wheels including a planet and sun gear arrangement provide the facility to accept a direct mechanical count input as well as a carry-over transfer input from the next lower order wheel. The gear arrangement is relatively complex and difficult to assemble.
Other designs of counting or registering mechanisms are shown in British Patent Specification No. 735 443 published in 1955, U.S. Pat. No. 4,015,109 (Deming) published 1977 and British Application Serial No. 2 024 478 published in 1980. U.S. Pat. No. 2,510,350 (Rouan and Knauer) shows a registering mechanism connected to a value setting mechanism in a postage meter.
In counter mechanisms in postage meters, the possibility must be provided for resetting the mechanism, when extra credit is purchased from the appropriate authority. The resetting means must be arranged to be secure so as to prevent fraudulent resetting. Typically, the resetting means includes a rotatable shaft with an operating knob behind a normally locked and/or sealed door in the housing. Rotation of the shaft typically causes only the higher three orders to be reset, the shaft itself acting on the lowermost of the three and the other two being stepped on by their carry transfer mechanisms. Thus it is only possible to purchase postal credit in comparatively large increments, there typically being another four non-resettable lower order wheels provided in such a mechanism. If the mechanism was modified to extend the resetting means to act on the lower order number wheels as well, in order to make credit purchase more flexible, the resetting shaft would then need to be rotated a very considerable number of times to reset the higher order numbers, which would be impractical.